This article provides the process to synchronize the account data from the Kerio Connect server manually.
You may need to do this when the source
.eml file (an EML file is an email, calendar event, task, or contact) is manually removed from the server-side, but it is still visible in the KOFF profile.
Open Outlook and navigate to the Send/Receive tab.
Click the Send/Receive All Folders button.
A pop-up window appears with the status bar showing the download progress of the new server changes. Wait for it to complete.
The KOFF profile is synced, and the server changes (.eml file's deletion) are applied correctly.
Microsoft article on sending messages immediately and checking for new mail.